1. Field of the Invention
This invention relates to a method and apparatus for manufacture of a continuous sheet of flat glass by supporting molten glass on a pool of molten metal and advancing it along the surface of the pool of molten metal while cooling it to form a continuous sheet of flat glass. More particularly, this invention relates to a method for controlling the flow of tin which is drawn along with the molten glass as it advances through the molten metal bath.
2. Discussion of the Prior Art
It has been proposed in the prior art that various types of barriers or dams be utilized to restrict the flow of the metal in the molten metal bath as the float glass is formed and cooled on the bath. The references described below are representative of the devices which are pertinent to the instant invention.
The U.S. Pat. No. 3,930,829 to Sensi discloses an arrangement of dams both in the transverse and longitudinal direction to control the movement of tin in a molten bath for glass formation. The dams of Sensi are extended from the bottom of the chamber and may closely approach the surface of the glass.
U.S. Pat. No. 3,930,828 to Kunkle discloses another system of dams to divide the molten metal of a float glass-forming tank into compartments which may be individually cooled or heated in order to regulate the forming process.
U.S. Pat. No. 3,607,199 to Itakura discloses a U-shaped dam near the forming region that acts to control the flow of molten metal in a region directly adjacent an entry location of glass into a float bath.
U.S. Pat. No. 3,483,617 to Lawrenson discloses a series of buoyant depressible barriers which are adapted to raise against the bottom of float glass being formed and thereby restrict the movement of tin or other molten metal longitudinally without interfering with the advancement of float glass through the bath.
The above systems while aiding in control of tin movement which introduces some defects in float glass do not effectively inhibit longitudinal distortion which is believed caused by the movement of tin within the bath closely adjacent the lower surface of the glass as it moves through the bath .This tin becomes unevenly heated in the transverse direction and leads to the longitudinal distortion defect.
The system of Lawrenson while inhibiting some flow of metal closely with the bottom of the glass has not proven feasible as the barriers may tend to cause defects when they scrape on the bottom surface of the floating glass as it hardens. Further, at times the barriers are depresed by the flow of the tin or other molten metal and therefore allow the tin flowing with the glass to pass over them and therefore do not prevent longitudinal defects.